The disclosure relates to a hydraulic or pneumatic (fluidic) drive provided for the actuation of fittings which have a switching or regulating valve, which drive comprises a control cylinder and a safety circuit which, in a line to which a cylinder chamber of the control cylinder is connected, has two shut-off valves connected in series with one another. The fitting may be used for example in a power plant, in the chemical or petrochemical industry, in the field of oil and gas delivery etc. Fittings are for example servo-operated safety valves, fast-closure valves, fast-opening valves, regulating fittings, fast-closure flaps, pilot valves, internal-medium-controlled isolating valves in power plants, valves for mixing identical or different substances, etc.
DE-B 2 025 836 discloses a hydraulic safety circuit for a double-acting hydraulic cylinder with two pressure chambers, in which, in the case of a fast shut-off, the two pressure chambers are connected to one another via a plurality of pilot-controlled seat valves connected in parallel with one another. The supply for the pilot control is provided either via a check valve from the pressurized chamber of the hydraulic cylinder or via a check valve from an external pressure source. Said safety circuit can tolerate failure of one of the parallel-connected seat valves during the fast shut-off.
It is known from U.S. Pat. No. 5,133,189 for in each case two safety valves connected in series with one another to be arranged in two fluid paths which, for safety reasons, run parallel to one another. The two parallel fluid paths are provided for a redundancy in the event of a fast shut-off of a steam valve. The series connection of two safety valves makes it possible for these to be tested individually for functionality during operation.
DE 10 2004 042 891 B3 discloses a safety circuit in which four logic valves are arranged in accordance with the basic principle of the above-cited U.S. Pat. No. 5,133,189. A pressure chamber of a working cylinder can, in an emergency, be relieved of pressure via two relief lines running parallel to one another. In each relief line are provided two logic valves arranged in series with one another, of which one is an active logic valve and the other is a passive logic valve.
A disadvantage of such safety circuits is that each passive logic valve can be tested only together with the active logic valve of the parallel line. For this purpose, a connecting line with a throttle is provided between the two parallel lines.
By contrast to this, it is the object of the disclosure to provide a hydraulic or pneumatic (fluidic) drive for the actuation of fittings with a switching or regulating valve, which drive has the features of the disclosure and in which drive the safety-relevant function of the shut-off valves can be tested even individually at any time without it being necessary for the safety circuit or the regulating or switching valve or the system to be put out of operation for this purpose.
Said object is achieved by means of a hydraulic or pneumatic drive, or generally by a fluidic drive, having the features of the disclosure.